Derby is a city in New Haven County, Connecticut, United States. The population was 12,391 at the 2000 census. With 5 square miles (13 km2) of land area, Derby is Connecticut's smallest municipality.
The city has a Metro-North railroad station called Derby – Shelton.
Derby was settled in 1642 as an Indian trading post under the name Paugasset. It was named after Derby, England in 1675.